Dark Matter and dimensions

[Daecon]

String theory postulates that there are more than three spacial dimensions, I forget exactly how many (it's been a while since I read up on the theory) but is it 11 more dimensions or 11 dimensions in total, or something like that?

 

Anyway, it's been suggested that the reasons these extra dimensions can exists without us knowing about them could be because they're curled up on themselves and are really really small.

 

Dark Matter is supposed to account for about 75% or so of the mass of the Universe that we can't detect, what if the reason we can't detect it is because it's confined to these other dimensions within the Universe?

 

In an analogy of a 2-d creature being unable to detect anything along a 3rd dimension, what if our 3-d existence means we're just unable to detect this extra matter because it's outside of our detectional perspective?

 

What I'm speculating is this, instead of these extra dimensions being curled up too small to detect, they're as large as our regular 3 dimensions, and that our "Dark Matter" is actually just ordinary matter, but confined to these other dimensions but just separate from us because these other dimensions don't interact with the EM spectrum.

[ajb]

Your speculation sounds like a brane-world scenario in which dark matter is matter on another brane separate from ours and as such it can only interact gravitationally with us. Such scenarios have been proposed before and analysed.

 

I expect Martin maybe able to say more about string and brane cosmologies? You could search the Arxiv for more also.

Edited January 15, 2009 by ajb

[Daecon]

Really? Cool.

 

If this is actually a theoretical plausibility, could this be transferred to one of the more serious forums by the mods, or is it best kept here?

[Daecon]

So what problems are most obvious (but not to me) in this idea?

[Severian]

Well, the biggest issue I would have with it is that it is a sledgehammer to crack a nut. Normally one would use extra dimensions and branes to try and explain why some particles feel some interactions and not others. So, for example, some particles might feel electromagnetism, while others feel only gravity.

 

This is indeed what you are suggesting - dark matter is on a particular brane where the SM gauge symmetry does not apply, so it feels only gravity.

 

Fair enough, but the phenomenology (what we would see in experiment) can equally well be expressed by just saying the dark matter has no charge, no SU(2) isospin and no color. That's it!

 

So we have a simpler (if less elegant) description of matter. Now, if your brane model can make other predictions about the universe and get them right, that would be a whole different ball game. Unfortunately it can't.

[Daecon]

Aha, I see. Occam's razor.

 

I've just had another thought that's marginally related...

 

Is the rate and duration of a Hawking radiation sufficient to account for all the matter that is absorbed by the black hole? Would all the matter sucked in throughout the black hole's life eventually be converted into Hawking radiation?

 

If that isn't the case, and black holes have been happening throughout most of the Universe's life with matter being sucked in and crushed into a singularity... What if black holes funnel this matter through the singularity (instead of into it) and it comes out the "other side" into the non-EM dimensional side of the Universe?

 

The sludge of crushed matter would be expelled from the black hole at the same speed it's been sucked in, giving it enough momentum to disperse around the same area as the parent galaxy, with it's gravity being sufficient to hold "our" matter in a stable galaxy-sized shape.

 

Hmm... although I've not really been able to think of a decent resolution to the gravitational impact of the black hole itself in the non-EM dimensions. Maybe the speed of light is different (if light were able to interact with these dimensions) and that the force of expulsion from the black hole is sufficient to break free from where the event horizon would be on our side.

 

This conjecture is getting complicated. Maybe it's best to keep it in this forum.